The first form, with an argument, defines your player to have the gender . If is one of the standard genders (e.g., 'male', 'female', 'neuter',...), your various pronouns will also be set appropriately, making exits and certain other objects behave more pleasantly for you.
The second form tells you the current definition of your player's gender, your current pronouns, and the complete list of standard genders.
It should be noted that some of the "genders" on the standard gender list need verb conjugation in order to work properly and much of the MOO isn't set up for this (...yet). For example, you should expect to see `they is' a fair amount if you @gender yourself `plural'. *Last Updated: 06/12/18 by Fengshui*